Compact compensating cylinder

ABSTRACT

A compensating cylinder unit for compensating relative movements between a stationary frame and a compensated frame which includes parts of a coiled tubing compensation system. The compensating cylinder unit includes a fluid reservoir configured to connect to the stationary frame, and a compensating cylinder configured to connect to the compensated frame, to at least partly enclose the fluid reservoir, and to be in a fluid communication with the fluid reservoir to allow for an axial displacement of the compensating cylinder relative to the fluid reservoir.

CROSS REFERENCE TO PRIOR APPLICATIONS

This application is a U.S. National Phase application under 35 U.S.C.§371 of International Application No. PCT/EP2015/053248, filed on Feb.17, 2015 and which claims benefit to Norwegian Patent Application No.20140255, filed on Feb. 27, 2014. The International Application waspublished in English on Sep. 3, 2015 as WO 2015/128217 A1 under PCTArticle 21(2).

FIELD

The present invention relates generally to the field of floatingoffshore platforms or vessels for the exploitation of undersea depositsof petroleum and natural gas. The present invention more specificallyrelates to compensating cylinders for compensating relative movementswithin a coiled tubing compensation system.

BACKGROUND

Coil tubing provides a rig crew with a quick and easy access to livewells in order to perform various well intervention operations. The coiltubing equipment generally consists of a coiled tube, a drive unit, anda control cabinet. The equipment is normally not fixed to one rig, butcan be transported between various locations. The coil tubing has a longtrack record for onshore land drilling, where the implementation isfairly simple. When used offshore on floating drilling units, it mustalso have some sort of compensation. With a traditional derrick with adrill string compensator or a ram rig system, the drive unit of the coiltubing is supported in a fixed coil tubing unit. This is hung up ineither the elevator or the bails. Many of the latest rigs havesubstituted the regular drill string compensator with an activecompensated drawwork. This is, however, not suitable for the morefragile operations like coil tubing. Any abruption of the activecompensation when the coil tubing is fixed to seabed may easily destroythe coil tubing. The coil tubing frame itself must have a compensatingfeature in such cases.

There have been some recent proposals to address the challenge ofobtaining active compensation while providing a satisfactory low risk ofabruption. WO 2005/061803 describes an inline compensator with twopassive cylinders on a frame replacing the vertical beams. US2012/0227976 A1 describes a similar solution.

Common for the previously-described compensation systems is that thepressure vessels are not located on the compensating unit itself. Thesupply of compressed air to drive the compensation motion is furthermoreperformed by one or two relatively large size hoses, which is highlyunfavorable for safety reasons.

SUMMARY

An aspect of the present invention is to provide a less space demandingyet secure compensating cylinder when installed in a system such as in acoil tubing system. Another aspect of the present invention is toprovide a less space demanding compensating cylinder also afterdecoupling from the operational system, for example, during transport.

In an embodiment, the present invention provides a compensating cylinderunit for compensating relative movements between a stationary frame anda compensated frame which includes parts of a coiled tubing compensationsystem. The compensating cylinder unit includes a fluid reservoirconfigured to connect to the stationary frame, and a compensatingcylinder configured to connect to the compensated frame, to at leastpartly enclose the fluid reservoir, and to be in a fluid communicationwith the fluid reservoir to allow for an axial displacement of thecompensating cylinder relative to the fluid reservoir.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in greater detail below on the basisof embodiments and of the drawings in which:

FIG. 1 shows a cross sectional side view of a compensated coil tubingframe in accordance with the present invention, including a supportstructure and a coiled tubing rigup;

FIG. 2A shows a cross sectional side view of a compact compensatingcylinder unit in accordance with the present invention in an operationalmode, where the accumulator assembly is stroked in an intermediateposition relative to the surrounding compensating cylinder;

FIG. 2B shows a cross sectional side view of a compact compensatingcylinder unit in accordance with the present invention in an operationalmode, where the accumulator assembly is stroked in an intermediateposition relative to the surrounding compensating cylinder;

FIG. 2C shows a cross sectional side view of a compact compensatingcylinder unit in accordance with the present invention in an operationalmode, where the accumulator assembly is stroked in an intermediateposition relative to the surrounding compensating cylinder;

FIG. 2D shows a cross sectional side view of a compact compensatingcylinder unit in accordance with the present invention in an operationalmode, where the accumulator assembly is stroked in an intermediateposition relative to the surrounding compensating cylinder;

FIG. 3A shows a side view of a compact compensating cylinder unit inaccordance with the present invention in an operational mode, theaccumulator assembly being stroked in an upper position relative to thesurrounding compensating cylinder;

FIG. 3B shows a side view of a compact compensating cylinder unit inaccordance with the present invention in an operational mode, theaccumulator assembly being stroked in an upper position relative to thesurrounding compensating cylinder;

FIG. 4A shows a side view of a compact compensating cylinder unit inaccordance with the present invention in an operational mode, theaccumulator assembly being stroked in a lower position relative to thesurrounding compensating cylinder;

FIG. 4B shows a side view of a compact compensating cylinder unit inaccordance with the present invention in an operational mode, theaccumulator assembly being stroked in a lower position relative to thesurrounding compensating cylinder;

FIG. 5A shows a side view of a compact compensating cylinder unit inaccordance with the present invention in a retracted transport mode;

FIG. 5B shows a side view of a compact compensating cylinder unit inaccordance with the present invention in a retracted transport mode; and

FIG. 5C shows a side view of a compact compensating cylinder unit inaccordance with the present invention in a retracted transport mode.

DETAILED DESCRIPTION

The present invention in particular relates to a compensating cylinderunit suitable for compensating relative movements between a stationaryframe and a compensated frame constituting parts of a coiled tubingcompensation system, where the compensated frame is connected to thecompensating cylinder. All the necessary tools for the coiled tubingsystem may be arranged on the compensated platform in order to providecompensation of vertical movements during operation. The cylinder unitcomprises a compensating cylinder suitable for connection to thecompensated frame and a fluid reservoir suitable for connection to thestationary frame, wherein the compensating cylinder is in fluidcommunication with the fluid reservoir to allow for an axialdisplacement of the compensating cylinder relative to the fluidreservoir. The compensating cylinder is furthermore characterized inthat it at least partly encloses the fluid reservoir.

In an embodiment of the present invention, the cylinder unit can, forexample, further comprise a gas reservoir having a second gas reservoirend and a connection element fixed to the second gas reservoir end andarranged into an opening within a first fluid reservoir end of the fluidreservoir, creating an axial interconnection between the gas reservoirand the fluid reservoir, wherein the cylinder is slidingly arrangedaround the circumference of the connection element. The connectionelement may display at least one pressure equalizing channel enablingfluid communication between the reservoirs. The connection element mayfurthermore comprise an outward protruding piston flange, wherein theconnection element releasably interconnects the second gas reservoir endto the first fluid reservoir end through abutment of an outer radialsurface of the protruding piston flange against an inner radial surfaceof the first fluid reservoir end.

In an embodiment of the present invention, a first fluid reservoir endof the fluid reservoir can, for example, comprise an outward protrudingfluid reservoir flange.

In an embodiment of the present invention, the cylinder unit can, forexample, further comprise a gas reservoir, wherein the cylinder, the gasreservoir and the fluid reservoir are mutually displaceable in the axialdirection, the displacements being confined between an operationalconfiguration where the gas reservoir is locked to the fluid reservoirand a transport configuration where the outer surface of a first fluidreservoir end of the fluid reservoir abuts the inner surface of a firstcylinder end of the cylinder, and where the gas reservoir is axiallyreleased from the fluid reservoir. The term “locked” is defined as thesituation where the gas reservoir is immovable or almost immovablerelative to the fluid reservoir. The cylinder unit may further comprisea connection element fixed to a second gas reservoir end of the gasreservoir and arranged into an opening within a first fluid reservoirend of the fluid reservoir so as to create an axial interconnectionbetween the gas reservoir and the fluid reservoir, and where thetransport configuration includes abutment of the surface of theconnection element towards the inner surface of a second fluid reservoirend of the fluid reservoir.

In an embodiment of the present invention, the cylinder unit can, forexample, further comprise a fluid channel enabling fluid communicationbetween the fluid reservoir and a volume within the cylinder situatedoutside the fluid reservoir. The fluid channel may extend from a secondfluid reservoir end of the fluid reservoir to the volume within thecylinder situated outside the fluid reservoir. The fluid channel mayfurther comprise a through-going accumulator passage penetrating thesecond fluid reservoir end. The fluid channel may further comprise afluid guiding feeding tube extending from a second fluid reservoir endof the fluid reservoir within the fluid reservoir.

In an embodiment of the present invention, the cylinder unit can, forexample, further comprise a gas reservoir comprising a second gasreservoir end and a connection element fixed to the second gas reservoirend comprising a radial channel, where the connection element isarranged into an opening within a first fluid reservoir end of the fluidreservoir so as to create an axial interconnection between the gasreservoir and the fluid reservoir. The fluid guiding feeding tube mayfurther comprise at least one radial bore being alignable to the atleast one radial channel to enable fluid communication between thefeeding tube and a volume within the cylinder situated outside the fluidreservoir and the gas reservoir. Note that there is no fluidcommunication between the pressure equalizing channel(s) and the radialchannel(s).

In an embodiment of the present invention, the axial walls of thecompensating cylinder can, for example, slidingly surround theconnection element, the second gas reservoir end, and the first fluidreservoir end, so as to form a fluid tight first cylinder chamberbounded by at least inner walls of the cylinder, the outer walls of thegas reservoir, and an outer radial surface of the first fluid reservoirend facing a first axial cylinder end of the cylinder. Note that “fluidtight” must be interpreted in accordance with the prevailingrequirements of the technical field in question. The first fluidreservoir end may comprise an outwardly protruding fluid reservoirflange creating a second cylinder chamber bounded by at least the innerwalls of the cylinder, the outer walls of the fluid reservoir, and anouter radial surface of the protruding fluid reservoir flange of thefirst fluid reservoir end facing away from the first fluid reservoirend. The volume of the second cylinder chamber can be less than thevolume of the first cylinder chamber. The second cylinder chamber canfurthermore be connected to a pressure control device which enablespressure adjustments within the second cylinder chamber, for example, anexternal accumulator and/or an active control system.

In an embodiment of the present invention, the cylinder unit can, forexample, further comprise a fluid channel enabling fluid communicationbetween the fluid reservoir and the first cylinder chamber, where thefluid channel comprises a through-going accumulator passage penetratinga second fluid reservoir end of the fluid reservoir, a valve devicearranged outside the fluid reservoir in fluid communication with thethrough-going accumulator passage, and a fluid guiding feeding tubecomprising a first longitudinal end arranged in fluid communication withthe first cylinder chamber during operation and a second longitudinalend arranged in fluid communication with the valve device.

The present invention also provides a method for altering a compensatingcylinder unit from an operational configuration to a transportconfiguration, which compensating cylinder unit comprises a compensatingcylinder, a fluid reservoir, and a gas reservoir interconnected in fluidcommunication with the fluid reservoir. The compensating cylinder is influid communication with the fluid reservoir in order to allow for anaxial displacement of the compensating cylinder relative to the fluidreservoir. The method comprises the steps of:

venting the volumes within the compensating cylinder and both reservoirsto an ambient pressure;

optionally releasing the interconnection between the gas reservoir andthe fluid reservoir; and

applying an external contraction force on one or both axial sides of thecylinder unit to axially displace the gas reservoir relative to thefluid reservoir.

The compensating cylinder unit used in the method may be in accordancewith the compensation cylinder described above.

The present invention also provides a coiled tubing compensation systemcomprising a stationary frame, a compensated frame, and a compensatingcylinder unit in accordance with the cylinder unit described above,wherein the stationary frame connects to the fluid reservoir and thecompensated frame connects to the compensating cylinder. The system maycomprise at least two compensating cylinder unit having theirlongitudinal axes arranged in parallel. The term “stationary” meansstationary relative to an underlying platform or vessel.

Numerous specific details are introduced in the following description toprovide a thorough understanding of, and an enabling description for,embodiments of the claimed apparatus and method. One skilled in therelevant art will recognize, however, that these embodiments can bepracticed without one or more of the specific details, or with othercomponents, systems, etc. In other instances, well-known structures oroperations are not shown, or are not described in detail, to avoidobscuring aspects of the disclosed embodiments.

FIG. 1 shows the main components of a coiled tubing system 30 inaccordance with the present invention. The coiled tubing system 30comprises a coiled tubing machine (injector head) 31 containing themechanism to push and pull a coiled tubing pipe or string 34 in and outof a well (not shown). The coiled tubing machine 31 has a curved guidebeam 32 on top, often called a guide arch or gooseneck, which threadsthe coiled tubing pipe 34 into the body of the coiled tubing machine 31.A blowout preventer (BOP) 33 may be arranged to form an intermediatecomponent between the coiled tubing machine 31 and the coiled tubingpipe 34. The BOP 33 may cut the coiled tubing pipe 34 with subsequentsealing. Components 31-34 are supported on a compensated frame 50 whereeach longitudinal end is connected to a compensating cylinder 1 of aninventive compensating cylinder unit 100 having the ability tocompensate for environmentally induced forces such as sea current or seawaves. The compensating cylinder unit 100 thus forms an integral part ofthe coiled tubing system 30. The two longitudinal ends 10 a, 5 b of eachcompensating cylinder unit 100 are connected to a common top frame 60and a common lower support frame 40, respectively. As will be apparentfrom the description below, the accumulator and pressure vessels 5,10are included into the compensating cylinder 1. There is thus no need forlarge hydraulic or pneumatic hoses to external sources. The top frame 60interfaces the lifting equipment in the derrick, and the lower supportframe 40 may rest on deck. The structure that bonds the two cylindertubes together will now function as a compensated platform for where toplace all the necessary tools for the coil tubing system. Thisparticular configuration separates this arrangement to a large degreefrom similar prior art systems which must be lifted well clear of thedrill floor (not shown).

FIG. 2A shows a principal side view sketch of the compensating cylinderunit 100 in accordance with the present invention. A pressure vessel 10and a fluid accumulator 5 are interconnected via a central piston 2,forming an accumulator assembly. The central piston 2 is fixed to alower axial vessel end 10 b of the pressure vessel 10 and is releasablyfixed to a protruding upper axial accumulator end 5 a of the fluidaccumulator 5. The latter connection may be obtained by maintaining aprotruding piston flange 14 pushed towards the inner surface ofprotruding upper axial accumulator end 5 a by pressure or other suitablemeans. The fluid accumulator 5 and the pressure vessel 10 are furtherslidingly journaled into a common compensating cylinder or barrel 1,forming a closed annulus cylinder chamber between the inner wall of thecompensating cylinder 1 and the outer wall of the journaled accumulatorassembly 5,10. The cylinder chamber is divided into an upper cylinderchamber 1′ and a lower cylinder chamber 1″ by the protruding upper axialaccumulator end 5 a. The other longitudinal ends of the upper and lowercylinder chambers 1′,1″ are bounded by an upper axial cylinder end laand a lower axial cylinder end lb, respectively. One or morethrough-going axial drillings 6 are provided into the central piston 2in order to provide fluid communication between the interior of thepressure vessel 10 and the interior of the fluid accumulator 5. A fluidchannel 8 (FIG. 2B) is further provided to run from the interior of thefluid accumulator 5 to the upper cylinder chamber 1′. This fluid channel8 comprises:

-   -   a lower end accumulator drilling 12 penetrating a lower axial        accumulator end 5 b;    -   a suitable feeding tube 11 comprising upper and lower        longitudinal ends 11 a, 11 b arranged from the lower axial        accumulator end 5 b to at least near the lower axial vessel end        10 b;    -   a valve device 13 providing a controllable fluid communication        between the lower accumulator drilling 12 and the feeding tube        11; and    -   one or more radial oriented bores 20 arranged at an upper        longitudinal end 11 a of the feeding tube 11 providing fluid        communication between the interior of the feeding tube 11 and        the upper cylinder chamber 1′.

FIG. 2B provides further operational details of the compensatingcylinder unit 100 indicating by arrows the pathway of the fluid channel8. The fluid accumulator 5 in FIG. 2B is illustrated as partly filledwith pressurized fluid 22, while the pressure vessel 10 is illustratedas filled with pressurized gas 21 (for example, air). Due to thethrough-going axial drillings 6, the pressures in the pressure vessel 10and the fluid accumulator 5 are equalized. If the valve device 13 isopened, the pressurized fluid 22 is forced through the fluid channel 8into the upper cylinder chamber 1′ via the axial feeding tube 11 and theradial bores 20. As a result, the pressure in the pressurized fluid 22is converted to a force within the upper cylinder chamber 1′ of thecylinder 1 that equals the effective chamber or annulus area times thefluid pressure. The axial force components (F_(a)) acting on the innersurface of an upper axial cylinder end la of the cylinder 1 and theouter surface of the protruding upper axial accumulator end 5 a cause avertical motion of the cylinder 1 when the fluid accumulator 5 is fixedto a rigid support such as a compensated frame 50 (FIG. 1). For example,if the axial (or vertical) force components (F_(a)) within the uppercylinder chamber 1′ increases due to increased pressure within the fluidchannel 8, the accumulator assembly 5,10 moves along the axial directionof the cylinder 1 away from the upper cylinder end 1 a. Likewise, if theaxial (or vertical) force components (F_(a)) within the upper cylinderchamber 1′ decreases due to decreased pressure within the fluid channel8 and the fluid accumulator 5, the accumulator assembly moves along theaxial direction of the cylinder 1 towards the upper cylinder end 1 a. Acompensating effect similarly to the effect of the prior artcompensating cylinders is consequently achieved, but with a more compactcompensating cylinder unit 100.

Due to the different outer diameters of the pressure vessel 10 and thefluid accumulator 5, the forces acting in the upper cylinder chamber 1′is in general larger than the forces acting in the lower cylinderchamber 1″. The lower cylinder chamber 1″ may be connected to a lowpressure accumulator to keep the chamber volume oil-filled andlubricated. It may, however, also (or alternatively) be used to activelycontrol the compensation in a similar way as, for example, in lowpressure accumulator of prior art dual acting type cylinders. By addingan active control loop such as a hydraulic control loop to the lowercylinder chamber 1″, the force of the overall cylinder tensioning may becontrolled by use of active means. The nature of a regular passivecylinder is that the pressure in the pressure vessel often varies withthe position of the compensator stroke, which in general is undesired.The effect can be neutralized, or nearly neutralized, via the mentionedcontrol loop, resulting in a cylinder providing a more stablecompensating force throughout the stroke length compared with cylinderswithout active control loops.

An about 1:22 scale side view drawing of an operational compactcompensating cylinder unit 100 in an intermediate stroke position and acorresponding sectional drawing along line B-B is shown in FIGS. 2C and2D, respectively. The valve device 13 providing controlled fluidcommunication between the lower accumulator drilling 12 and the feedingtube 11 is partly illustrated in FIG. 3D.

FIGS. 3A and 3B show side view drawings of the same operationalcompensating cylinder unit 100 as in FIGS. 2C and 2D (the latter alongD-D) but where the accumulator assembly 5,10 is stroked in an upperposition relative to the surrounding compensating cylinder 1, i.e., aposition where the outer radial surface of the protruding upper axialaccumulator end 5 a abuts the inner radial surface of the upper cylinderend la due to increased pressure force (F_(a)) within the first cylinderchamber 1′. FIGS. 4A and 4B also show side view drawings as in FIGS. 2C,3A,2D, and 3B, respectively (FIG. 4B seen along C-C of FIG. 4A), butwhere the accumulator assembly 5,10 is stroked in a lower positionrelative to the surrounding compensating cylinder 1, i.e., a positionwhere the outer radial surface of the protruding upper axial accumulatorend 5 a facing towards the lower axial accumulator end 5 b abuts theinner radial surface of the lower cylinder end lb due to decreasedpressure force (F_(a)) within the first cylinder chamber 1′.

FIG. 5A shows a principal side view sketch of the compensating cylinderunit 100 in accordance with the present invention and arranged in aretracted transport mode, i.e., a position where the outer radialsurface of the protruding upper axial accumulator end 5 a abuts theinner radial surface of a first cylinder end la, while the radialsurface of the central piston 2 abuts the inner radial surface of thelower axial accumulator end 5 b. This transport configuration or modemay be obtained by axially releasing the pressure vessel 10 from thefluid accumulator 5, for example, by venting the volumes within thecompensating cylinder 1, the fluid accumulator 5 and the pressure vessel10 to an ambient pressure and/or imparting an axial force on thecylinder unit 100, thereby enforcing an axial movement of the fluidaccumulator 5 into the pressure vessel 10. Note that the central piston2 on the pressure vessel 10 may be releasably connected to the fluidaccumulator 5 by means other than, or in addition to, pressure inducedconnection, for example, via various mechanically-releasable couplingdevices. An about 1:22 scale side view drawing of a compact compensatingcylinder unit 100 as in FIG. 5A, i.e., retracted transport mode, and acorresponding sectional drawing along line A-A is shown in FIGS. 5B and5C, respectively.

In the preceding description, various aspects of the system and methodaccording to the present invention have been described with reference tothe illustrative embodiment. For purposes of explanation, specificnumbers, systems and configurations are set forth in order to provide athorough understanding of the apparatus and its workings. However, thisdescription is not intended to be construed in a limiting sense. Variousmodifications and variations of the illustrative embodiment, as well asother embodiments of the apparatus, which are apparent to personsskilled in the art to which the disclosed subject matter pertains, aredeemed to lie within the scope of the present invention. Referenceshould also be had to the appended claims.

LIST OF REFERENCE NUMERALS

-   F_(a) Axial/vertical force component/pressure force-   1 Compensating cylinder/barrel-   1′ First cylinder chamber/upper cylinder chamber-   1″ Second cylinder chamber/lower cylinder chamber-   1 a Upper cylinder end/upper axial cylinder end/first cylinder end-   1 b Lower cylinder end/lower axial cylinder end-   2 Central piston/connection element-   5 Fluid accumulator/fluid reservoir-   5 a Protruding upper axial accumulator end/first fluid reservoir end-   5 b Lower axial accumulator end/second fluid reservoir end-   6 Axial drilling/pressure equalizing channel-   8 Fluid channel-   10 Pressure vessel/gas reservoir-   10 a Upper axial vessel end/first gas reservoir end-   10 b Lower axial vessel end/second gas reservoir end-   11 Fluid guiding feeding tube/feeding tube-   11 a Upper longitudinal end/first longitudinal end-   11 b Lower longitudinal end/second longitudinal end-   12 Lower end accumulator drilling/Through-going accumulator passage-   13 Valve device-   14 Protruding piston flange-   16 Protruding accumulator flange/protruding fluid reservoir flange-   20 Radial bore-   21 Pressurized gas-   22 Pressurized fluid-   23 Radial channel-   30 Coiled tubing system/Coiled tubing compensation system-   31 Coiled tubing machine/injector head-   32 Curved Guide beam/Guide Arch/Gooseneck-   33 Blowout Preventer (BOP)-   34 Coiled tubing pipe/Coiled tubing string-   40 Lower support frame/stationary frame-   50 Compensated frame-   60 Upper support structure/Top frame-   100 Compensating cylinder unit

What is claimed is: 1-20 (canceled)
 21. A compensating cylinder unit forcompensating relative movements between a stationary frame and acompensated frame comprising parts of a coiled tubing compensationsystem, the compensating cylinder unit comprising: a fluid reservoirconfigured to connect to the stationary frame; and a compensatingcylinder configured to connect to the compensated frame, to at leastpartly enclose the fluid reservoir, and to be in a fluid communicationwith the fluid reservoir to allow for an axial displacement of thecompensating cylinder relative to the fluid reservoir.
 22. Thecompensating cylinder unit as recited in claim 21, wherein, the fluidreservoir comprises a first fluid reservoir end which comprises anopening, and further comprising: a gas reservoir comprising a second gasreservoir end; and a connection element attached to the second gasreservoir end and arranged into the opening of the first fluid reservoirend of the fluid reservoir so as to provide an axial interconnectionbetween the gas reservoir and the fluid reservoir, wherein, thecompensating cylinder is further configured to slide around acircumference of the connection element.
 23. The compensating cylinderunit as recited in claim 22, wherein the first fluid reservoir end ofthe fluid reservoir further comprises a protruding fluid reservoirflange.
 24. The compensating cylinder unit as recited in claim 22,wherein the connection element comprises at least one pressureequalizing channel configured to enable a fluid communication betweenthe fluid reservoir and the gas reservoir.
 25. The compensating cylinderunit as recited in claim 22, wherein, the first fluid reservoir endfurther comprises an inner radial surface, the connection elementcomprises a protruding piston flange which comprises an outer radialsurface, and the connection element is configured to releasablyinterconnect the second gas reservoir end to the first fluid reservoirend through abutment of the outer radial surface of the protrudingpiston flange against the inner radial surface of the first fluidreservoir end.
 26. The compensating cylinder unit as recited in claim25, wherein, the first fluid reservoir end further comprises an outersurface, the compensating cylinder comprises a first axial cylinder endwhich comprises an inner surface, the compensating cylinder, the gasreservoir, and the fluid reservoir are each configured to be axiallydisplaceable, the axial displacements being confined between, anoperational configuration where the gas reservoir is locked to the fluidreservoir, and a transport configuration where the outer surface of thefirst fluid reservoir end abuts the inner surface of the first axialcylinder end of the compensating cylinder (1), and where the gasreservoir is axially released from the fluid reservoir.
 27. Thecompensating cylinder unit as recited in claim 26, further comprising: aconnection element comprising a surface, the connection element beingfixed to the second gas reservoir end of the gas reservoir and arrangedinto the opening of the first fluid reservoir end of the fluid reservoirso as to provide an axial interconnection between the gas reservoir andthe fluid reservoir, wherein, the fluid reservoir further comprises asecond fluid reservoir end which comprises an inner radial surface, andthe transport configuration includes an abutment of the surface of theconnection element towards the inner radial surface of the second fluidreservoir end of the fluid reservoir.
 28. The compensating cylinderunit) as recited in claim 27, wherein, the compensating cylindercomprises a volume, and further comprising: a fluid channel configuredto provide a fluid communication between the fluid reservoir and thevolume within the cylinder arranged outside of the fluid reservoir. 29.The compensating cylinder unit as recited in claim 28, wherein the fluidchannel is further configured to extend from the second fluid reservoirend) of the fluid reservoir to the volume within the cylinder situatedoutside the fluid reservoir.
 30. The compensating cylinder unit asrecited in claim 29, wherein the fluid channel comprises a through-goingaccumulator passage which is configured to penetrate the second fluidreservoir end.
 31. The compensating cylinder unit as recited in claim28, wherein the fluid channel further comprises a fluid guiding feedingtube configured to extend from the second fluid reservoir end of thefluid reservoir.
 32. The compensating cylinder unit as recited in claim31, wherein, the connection element further comprises at least oneradial channel, the connection element being arranged into the openingof the first fluid reservoir end of the fluid reservoir so as to providean axial interconnection between the gas reservoir and the fluidreservoir, wherein, the fluid guiding feeding tube comprises at leastone radial bore which is alignable to the at least one radial channel toprovide a fluid communication between the fluid guiding feeding tube andthe volume within the cylinder situated outside the fluid reservoir andthe gas reservoir.
 33. The compensating cylinder unit as recited inclaim 26, wherein, the gas reservoir further comprises outer walls, thefirst fluid reservoir end further comprises an outer radial surfacewhich is arranged to face the first axial cylinder end of thecompensating cylinder, and the compensating cylinder further comprisesinner walls and axial walls which are configured to slidingly surroundthe connection element, the second gas reservoir end and the first fluidreservoir end so as to form a fluid tight first cylinder chamber whichis bounded by at least the inner walls of the compensating cylinder, theouter walls of the gas reservoir, and the outer radial surface of thefirst fluid reservoir end facing the first axial cylinder end of thecompensating cylinder.
 34. The compensating cylinder unit as recited inclaim 33, wherein, the fluid reservoir further comprises outer walls,and the first fluid reservoir end further comprises a protruding fluidreservoir flange comprising an outer radial surface which is arranged toface away from the first fluid reservoir end, the protruding fluidreservoir flange being configured to provide a second cylinder chamberwhich is bounded by at least, the inner walls of the compensatingcylinder, the outer walls of the fluid reservoir, and the outer radialsurface of the protruding fluid reservoir flange of the first fluidreservoir end facing away from the first fluid reservoir end.
 35. Thecompensating cylinder unit as recited in claim 34, further comprising: apressure control device configured to provide pressure adjustmentswithin the second cylinder chamber, wherein, the second cylinder chamberis connected to the pressure control device.
 36. The compensatingcylinder unit as recited in claim 34, further comprising: a fluidchannel configured to provide a fluid communication between the fluidreservoir and the fluid tight first cylinder chamber, the fluid channelcomprising, a through-going accumulator passage configured to penetratethe second fluid reservoir end of the fluid reservoir, a valve devicearranged outside the fluid reservoir to be in a fluid communication withthe through-going accumulator passage, and a fluid guiding feeding tubecomprising a first longitudinal end arranged to be in a fluidcommunication with the fluid tight first cylinder chamber duringoperation, and a second longitudinal end arranged to be in a fluidcommunication with the valve device.
 37. A method for altering acompensating cylinder unit from an operational configuration to atransport configuration, the compensating cylinder unit comprising: acompensating cylinder comprising a first axial side and a second axialside, a fluid reservoir, and a gas reservoir interconnected in a fluidcommunication with the fluid reservoir, the compensating cylinder beingin fluid communication with the fluid reservoir to allow for an axialdisplacement of the compensating cylinder relative to the fluidreservoir, the method comprising: venting each of a first volume withinthe compensating cylinder, a second volume in the fluid reservoir, and athird volume in the compensating cylinder to an ambient pressure; andapplying an external contraction force on at least one of the firstaxial side and the second axial side of the compensating cylinder unitto axially displace the gas reservoir relative to the fluid reservoir.38. The method as recited in claim 17, wherein that the compensatingcylinder unit comprises: a fluid reservoir configured to connect to thestationary frame; and a compensating cylinder configured to connect tothe compensated frame, to at least partly enclose the fluid reservoir,and to be in a fluid communication with the fluid reservoir to allow foran axial displacement of the compensating cylinder relative to the fluidreservoir.
 39. A coiled tubing compensation system comprising: astationary frame; a compensated frame; and the compensating cylinderunit as recited in claim 21, wherein, the stationary frame is configuredto connect to the fluid reservoir, and the compensated frame isconfigured to connect to the compensating cylinder.
 40. The coiledtubing compensation system as recited in claim 19 comprising at leasttwo compensating cylinder units arranged so as to have their respectivelongitudinal axes arranged in parallel.